Since 2008, Mexico has challenged the labeling, saying the policies discriminated against their industry.

"The compliance panels found that modifications to the labeling measures adopted by the United States in 2016 either removed discriminatory treatment to Mexican tuna products or were justified as exceptions to WTO rules on the grounds they were necessary for the conservation of exhaustible natural resources," the panel report said.

Mexico is appealing the ruling.

During the past nine years of the fight, several WTO panels have determined that some portions of U.S. dolphin-safe requirements were inconsistent with trade rules.

The decision will likely stave off retaliatory measures by Mexico. In May the WTO said Mexico could impose $163 million a year in countermeasures after the United States failed to comply with a previous WTO ruling in 2013.

"Mexico acknowledged during the arbitration proceedings that it would be required to terminate these retaliatory actions if the second round of compliance proceedings were to result in a determination that the 2016 labelling measure brought the US into compliance with its WTO obligations," the report said.

The United States has long argued that its labeling requirements do not discriminate against any country.

"The WTO has made clear — once and for all — that U.S. regulations protecting the lives of dolphins are consistent with our international obligations," Brady said.

“While today’s ruling is a positive step, dolphin-saving policies should never have been challenged as a trade violation in the first place,” said Ben Beachy, director of the Sierra Club’s Responsible Trade Program.

"With Mexico appealing today’s ruling, we’re still not out of the woods," Beachy said.

The decision comes a day after President Trump, who has regularly criticized the WTO, told Fox News that the U.S. never wins cases.

"The WTO is a political institution, so this ruling may be motivated by a sense of self-preservation, given that the administration has spotlighted how WTO tribunals order countries to gut domestic policies based on unaccountable tribunals making up new obligations to which countries never agreed,” said Lori Wallach, director of Public Citizen’s Global Trade Watch.

Public Citizen has called on the Trump administration and the Mexican government to include language in the North American Free Trade Agreement (NAFTA) affirming the U.S. labeling program to avoid any future disputes.

"To make sure that the attack on dolphin-safe tuna ends once and for all, a formal and final settlement of the case safeguarding the policy must be part of NAFTA renegotiations,” Wallach said.